1. Field of the Invention
The present invention is related to a photography apparatus and a photography method that employs an imaging element such as a CCD to obtain image data sets having wide dynamic ranges.
2. Description of the Related Art
CCD's, which are imaging means employed in digital cameras, have narrower dynamic ranges than silver salt film. Therefore, overexposure and underexposure are likely to occur in images photographed by digital cameras. For this reason, there are known techniques for obtaining image data sets having expanded dynamic ranges that exhibit favorably reproduction properties over a wide range from high brightness to low brightness. In these techniques, imaging is performed with different exposure conditions to obtain an image having a large amount of data toward the high brightness side, and an image having a large amount of data toward the low brightness side, for example, and then the images are combined to obtain an expanded dynamic range image data set.
As an example of a technique for obtaining a plurality of image data sets with different exposure conditions, there is a method that utilizes a CCD, in which main pixels having high sensitivity and sub pixels of smaller areas than the main pixels and therefore have lower sensitivity but are less likely to be saturated are arranged, to change the exposure conditions for each image, as disclosed in Japanese Unexamined Patent Publication No. 2003-179819. Another example of such a technique is a method in which photography is performed employing different shutter speeds, to change the exposure conditions for each image, as disclosed in Japanese Unexamined Patent Publication No. 11 (1999)-155098.
Generally, in the case that the aforementioned techniques are employed to obtain a dynamic range expanded image data set having a dynamic range which is expanded n times that of an image obtained by standard photography, an image data set, which is photographed with the same amount of exposure as that during standard photography, and an image data set, which is photographed with an exposure amount 1/n times that during standard photography, are required. In the case that the dynamic range is to be expanded to 800% (8 times), for example, an image data set, which is photographed with the same amount of exposure as that during standard photography, and an image data set, which is photographed with an exposure amount ⅛ that during standard photography, are required. That is, it is necessary to decrease the exposure amount compared to that during standard photography, in order to greatly expand the dynamic range.
However, in the technique disclosed in Japanese Unexamined Patent Publication No. 2003-179819, the CCD having the main pixels and the sub pixels, which have different sensitivities, are used to perform photography to obtain two images at a certain exposure ratio. Therefore, the exposure ratio is uniquely determined by the sensitivity ratio between the main pixels and the sub pixels. Accordingly, the expansion rate of the dynamic range cannot be set freely.
In the technique disclosed in Japanese Unexamined Patent Publication No. 11 (1999)-155098, it is not possible to reduce the amount of exposure to a degree that exceeds the limit of possible shutter speeds. Therefore, there is a limit to the expansion rate of the dynamic range.